cc/gcc: do not build plugins for static toolchains

Plugins are shared objects, and when building a toolchain statically,
the gcc build system breaks havok (although there is no hard technical
reasons it should not be possible)...

And consequently, do not enable plugin supoprt in binutils.

Reported-by: Thomas Spurden <thomas@ado.is-a-geek.net>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

# MIPS specific config options

config ARCH_mips

    select ARCH_SUPPORTS_32

    select ARCH_SUPPORTS_64 if EXPERIMENTAL

    select ARCH_DEFAULT_32

    select ARCH_USE_MMU

    select ARCH_SUPPORTS_BOTH_ENDIAN

    select ARCH_DEFAULT_BE

    select ARCH_SUPPORT_ARCH

    select ARCH_SUPPORT_TUNE

    help

      The MIPS architecture, as defined by:

        http://www.mips.com/